The present invention relates, in general, to a switching device.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
Switching devices of a type involved here disconnect a line network from the power grid in the event of excess currents in the line network lasting for a presettable time, in order to prevent further supply of electric current. There are also switching devices which disconnect a line network from the power grid in the event of a short-circuit to prevent further supply of electric current. These switching devices have therefore a so-called overcurrent trigger device and/or a short-circuit trigger device, which upon actuation trigger a mechanical disconnect device which disconnects the switching contacts of the switching device and prevents further current flow. The overcurrent trigger device and/or a short-circuit trigger device typically operate mechanically on a mechanical trigger of the disconnect device. In addition to triggering the disconnect device with the trigger device, an actuating lever is typically provided which can be used to control the disconnect device for disconnecting the switching contacts.
When the switching contacts are disconnected, an arc is produced between the opening switching contacts due to the physical principle described by the induction law. During a short-circuit in a line network, very high currents in a range between about 5 kA and 25 kA can occur. When a short-circuit causes the switching device to switch off, the switching contacts must disconnect this very high electric current. The produced arc is also very strong and would destroy the switching device without special equipment provided on the switching device. These switching devices therefore have typically a so-called arc quenching chamber which steers the produced arc and removes energy until the arc is extinguished. To this end, the arc quenching chamber has a number of metal plates, which are also referred to as de-ionizing plates. These metal plates, which are typically identical, are in conventional switching devices arranged inside the arc quenching chamber in a uniform pattern and parallel to one another. This has the disadvantage that some of the metal plates are frequently stressed more by an arc than others, which causes the various metal plates inside an arc quenching chamber to wear down differently. As a result, some metal plates may be worn down to a degree where continued operational safety of the switching devices can no longer be ensured. This is even more dangerous because such faults cannot be identified through external visual inspection, so the user may simply assume that the switching device is still operating safely.
It would therefore be desirable and advantageous to provide an improved switching device which obviates prior art shortcomings and is reliable and safe in operation, even after being repeatedly switched off, and which has also low manufacturing costs.